The first monarch has already been sighted in Arkansas! Mrs. Brisco of Vera Kilpatrick Elementary wrote: "Spotted
the first monarchs this spring about 4:00 P.M in a field just east of the city limits of Texarkana, AR (33.48N,
-93.92 W). There were two monarchs - both heading almost due east. They appeared to be in good shape and were flying
quite well."

How Far From Mexico Has the Migration
Traveled?
Each week, plan to look at the latest map and find the forward edge of the migration.

Chose a sighting that is the farthest from the sanctuaries. Using the latitude and longitude
given in the migration data table, measure the monarch's distance from the sanctuaries. (The sanctuaries are located
at 19 N, -100W.)

First measure the distance on your map, using a ruler and the scale bar.

Challenge Question #18
"Assuming the monarch sighted in Arkansas (33.48N, -93.92 W) flew all the way from the Mexican sanctuaries
(19 N, -100W), how far did that butterfly fly?"

(To respond to
this question, please follow the instructions below.)
Only Two Clusters Remain in Sierra Chincua SanctuaryMeanwhile, back in the sanctuary
region Eligio Garcia reports: "On the 16th of March there were only one or two clusters of monarchs in the
Sierra Chincua sanctuary that had not yet left for migration. On the highway to Toluca, I saw many monarchs migrating
toward the north. These butterflies came from the Cerro Pelon sanctuary that is very near Zitacuaro. The butterflies
were heading more or less in the direction of the El Rosario sanctuary (which is to the north of Cerro Pelon)."
The Count is In!How Large Was This Winter's Monarch Population?
Each week, you've received Eligo's measurements from one sanctuary, the Sierra Chincua. We've seen how the numbers
of monarch trees varies over time, and how much the colony moves.

Once every winter, all of the colonies
are measured. This is done in December, because during the coldest time of year the butterflies are clustered
together most tightly. Like a snapshot in time, the annual winter measurements give scientists a chance to estimate
the size of the entire over-wintering population. Here are this winter's measurements, courtesy of Sr. Roberto
Solis the director of the Reserva Especial de la Biosphera Mariposa Monarca (REBMM):

How Many Millions of Monarchs in Mexico
This Year?
Using Dr. Calvert's estimate of 13,000,000 monarchs per hectare, you can estimate the number of monarchs that over-wintered
in Mexico this year. You can also compare the population size from one year to the next.

Challenge Question #19
"According to the data provided by Sr. Robero Solis, how many monarchs do you estimate were in Mexico during
the past 6 years?

Watching the Wings for Clues
In our March 8 update, Challenge Question #13 asked, "How might a person in Texas be able to tell if the monarchs
they see are from Mexico or are from the Texas over-wintering population?"

The fact is, we simply can't tell without killing the butterflies for chemical analysis. However, using a technique
he learned from Dr. Karen Oberhauser and Dr. Bill Calvert, Texas teacher Harlen Aschen and his wife are conducting
their own field research this year. They are exploring the many unanswered questions about migratory and over-wintering
populations in the Gulf Coast region.

Because monarchs' wings become worn and faded over time, they can estimate how old the monarchs are. Age is a clue
as to whether the butterflies might have recently emerged in Texas, or lived for many months and migrated from
Mexico.

Here are 3 monarchs they captured in their backyard last week. Look carefully at each butterfly, and read and
the descriptions the Aschens gave them. (See below.)

3/19/00 Port Lavaca, Texas (28.53 N, -96.68 W)
"The monarchs for the past three weeks have been behaving differently. The ones we tagged and released between
November and late February would be seen again for days, sometimes for weeks. Now, we tag and release and few are
seen again. They might be sighted within a few hours again, but seldom the next day anymore. All movement has
been from south to southwest heading north to northeast.

"We are beginning to notice 'loading' of eggs of the wild Asclepias viridis that we have been observing this
week 7 miles west of Port Lavaca. We hope everyone to the north and northeast of us is on the lookout for tagged
monarchs from Texas. They are also marked on both hind wings with a 'sharpie' (in blank ink)."

Coming Next Week: Weather and
Migration
Get ready to explore how monarch migration is related to wind and weather. Beginning next week, Dr. Bill Calvert
will help us look at weather maps and relate the conditions back to the week's migration.
How to Respond to Today's Monarch Challenge Questions|

IMPORTANT: Please answer ONLY ONE
question in each e-mail message!

1. Address an e-mail message to: jn-challenge-monarch@learner.org
2. In the Subject Line of your message write: Challenge Question #18 (#19 or #20).
3. In the body of the EACH message, answer ONE of the questions above.